Uncaught TypeError: undefined is not a function

Question

我是一个相当初级的程序员，如果这个问题的解决方案相当简单，请原谅（尽管我已经努力寻找已经发布的解决方案）。我正在尝试面向对象的编程，但是当运行程序 "Uncaught TypeError: undefined is not a function" 在第 14 行时收到此错误消息。

var Gladiator = Object.create(null);
Gladiator.prototype = {
  becomeGladiator: function(attack, defense, hitPoints, name) {
    this.attack = attack;
    this.defense = defense;
    this.hitPoints = hitPoints;
    this.name = name;
  },
};

var Human = Object.create(Gladiator.prototype); 
Human.prototype = {
  becomeHuman: function(attack, defense, hitPoints, name) {
    this.becomeGladiator(attack, defense, hitPoints, name); //Error here
};
var ethan = Object.create(Human.prototype);
ethan.becomeHuman(14, 12, 15, "Ethan")

谢谢。

Answer 1

prototype 是属性函数（构造函数），用于在创建实例时设置内部 [[Prototype]] 属性。 Object.create 接受一个父对象并创建一个原型为父对象的对象；你只需要普通对象：

var Gladiator = Object.create(null);
Gladiator.becomeGladiator = function(attack, defense, hitPoints, name) {
  this.attack = attack;
  this.defense = defense;
  this.hitPoints = hitPoints;
  this.name = name;
};

var Human = Object.create(Gladiator);
Human.becomeHuman = function(attack, defense, hitPoints, name) {
  this.becomeGladiator(attack, defense, hitPoints, name); //Error here
};

var ethan = Object.create(Human);
ethan.becomeHuman(14, 12, 15, "Ethan");

Answer 2

如果您想知道为什么您的代码不起作用，这里有一个简短的解释：

ethan 继承自 Human.prototype 对象。
Human.prototype 继承自 Object.prototype 实例，因为它是使用对象的创建文字运算符 {}.
因此，当您执行 ethan.becomeHuman(..) 时，解释器会检查 ethan 是否有属性 becomeHuman。它不是。然后它在 ethan 继承自的对象上检查相同的对象，即 Human.prototype。这个现在确实有一个属性 becomeHuman 所以它被调用 this 关键字绑定到 ethan.
那么在进一步的执行中this.becomeGladiator就是ethan.becomeGladiator。现在，ethan 个实例没有名为 becomeGladiatar 的属性。它继承自 Human.prototype 实例，该实例也没有属性 becomeGladiator。 Human.prototype 继承自 Object.prototype，它都没有分配属性 becomeGladiatar。您已经检查了整个原型（继承）链但没有成功，这就是您收到错误的原因。

Uncaught TypeError: undefined is not a function

Uncaught TypeError: undefined is not a function

javascript

oop

prototype